Single crystal silicon is conventionally used as a material of a power semiconductor device that withstands high voltage and controls high current. Various types of power semiconductor device are present and each is used for a use suitable therefor. For example, a bipolar transistor and an IGBT (insulated gate bipolar transistor) respectively can handle a high current density but these transistors are not capable of high speed switching. Frequency limits of for the bipolar transistor and the IGBT are on the order of several kHz and about several 10 kHz, respectively.
On the other hand, a power MOSFET (metal oxide semiconductor field effect transistor) cannot handle high current but this MOSFET can be used at high speeds and at a frequency up to about several MHz. In the market, demand is strong for a power device that can simultaneously cope with high current and high speed. Therefore, efforts have been made to improve the IGBT and the power MOSFET. Therefore, at present, development has advanced to the extent that the performance limitations are substantially the limit of the materials. Investigations concerning materials from the viewpoint of a power semiconductor device have been conducted, and silicon carbide (hereinafter, referred to as “SiC”) has attracted attention as the next generation power semiconductor device because SiC is excellent in terms of low ON-voltage, high speed properties, and high temperature properties (see, e.g., Non-Patent Literature 1 below).
SiC is a highly stable material chemically, has a wide band gap of three eV, and can be used very stably as a semiconductor even at high temperatures. The highest electric field intensity thereof is also higher than that of Si by 10-fold or more. The same is true for gallium nitride (hereinafter, referred to as “GaN”), which is another wide band gap semiconductor material.
Similar to silicon, the wide band gap semiconductor enables fabrication of a Schottky barrier diode having a rectification property, by depositing a metal on the surface. Thus, a high voltage and low ON-resistance Schottky barrier diode can be realized using the wide band gap semiconductor as the material of the substrate.
Non-Patent Literature 1: “Optimum Semiconductors for High-Power Electronics”, IEEE Transactions on Electron Devices (Vol. 36, p. 1811, 1989)
Non-Patent Literature 2: “1200-V JBS Diode with Low Threshold Voltage and Low Leakage Current”, Materials Science Forum Vols. 600-603 (2009), pp. 939-942
Non-Patent Literature 3: “6.1.2 JBS Rectifier Structure: Reverse Leakage Model”, Silicon Carbide Power Devices: B. Jayant Baliga, p. 108
Non-Patent Literature 4: “4.3 Depletion Region”, Semiconductor Devices: S. M. Sze, pp. 93-99.